In the art of arc welding it has been found to be necessary to take steps to prevent the inclusion of contaminants such as water vapor in the weld. In particular, it has been observed that water vapor has a tendency to cause porosity in the weld area. A popular method of prevention has been to surround the welding tip with a shield of inert gas. In certan environments, however, it was found that the width of shield required resulted in a high volume rate of flow of the costly inert gas, so various other schemes for increasing the isolation of the weld from contaminants have been investigated. Among these have been several double-shield systems, such as Wempe, U.S. Pat. No. 2,903,559, which employs shielding gases other than air.